Inorganic cements exhibit characteristic properties of setting and hardening when mixed with water to form a paste. They are capable of joining rigid solid masses into coherent structures. Inorganic cements can be divided into hydraulic and nonhydraulic types according to the way in which they set and harden. For example, hydraulic cements are capable of setting and hardening in air and under water, whereas nonhydraulic cements are only capable of hardening in air. See Z. D. Jastrebski, The Nature and Properties of Enqineerinq Materials, 2d. Ed., John Wiley & Sons, New York (1977) at 356, the disclosure of which is incorporated by reference herein.
The most widely-used hydraulic cement is socalled Portland cement, which is obtained by heating an intimate mixture, composed mainly of calcareous and argillaceous materials, or other silica, alumina, and iron-oxide bearing materials, at a clinkering temperature of about 1400.degree. C. The partially sintered material, called clinker, is then ground to a very fine powder. After mixing with water, a hardened amorphous mass is formed consisting primarily of calcium-silicate hydrate (C--S--H) which, like other gels, contains a network of capillary pores and gel pores. The total porosity of a typical hardened Portland cement paste is about 30-40% by volume, having a very wide pore-size distribution ranging from 10-0.002 .mu.m in diameter. The gel porosity, consisting of very small pores, below 0.01 .mu.m, is about 26%, with the remaining porosity due to capillary network. See Z. D. Jastrebski, supra, at 356-61.
Portland cement formulations may also contain additional additives. For example, small amounts of calcium sulfate in the form of gypsum or anhydrite are added during grinding of the raw materials to control the setting time and enhance strength development of Portland cement. Cement pastes are sometimes impregnated with liquid organic monomers or liquid sulfur and polymerized to produce polymer-impregnated concrete. See 5 Kirk-Othmer Encyclopedia of Chemical Technology, 3rd. ed., John Wiley & Sons, New York (1978) at 163, the disclosure of which is incorporated by reference herein. Other additives include water reducers, plasticizers, air entrainment and anti-foaming additives, silica fines, fly ash, polymer latexes and the like.
Previously, in Applicants' U.S Pat. No. 4,930,428, the disclosure of which is herein incorporated by reference, a high strength concrete composition formed from water treated with about 0.5 to 100 parts per million (ppm) residual sodium tripolyphosphate (STP) was described. Surprisingly, the concrete composition was found to exhibit higher strength, density, and lesser porosity than conventional concrete compositions. This composition is a significant improvement over conventional concrete. However, as with conventional concrete, several disadvantageous properties remain.
Conventional concrete is not flexible or elastic. Thus, when conventional concrete is subjected to compressive, flexural, tensile and/or shearing forces, it breaks or cracks after undergoing relatively minor deformation. In addition, conventional concretes are relatively permeable and porous, and accordingly, often transport and retain a high degree of trapped moisture.
The tendency of conventional concrete to retain moisture can present particular problems in hot or cold climates. For example, moisture trapped in concrete during a period of freezing temperatures will expand and form ice crystals which often crack the concrete. This phenomenon, referred to as frost damage is particularly prevalent in areas subject to multiple freeze-thaw cycling. In such areas, the usable life of conventional concrete is often greatly reduced by this phenomenon. Furthermore, in an effort to overcome the tendency of conventional concrete to break or crack in these climates, conventional concrete is air entrained by the addition of various additives which increase the trapped air in the composition.
The relatively high permeability of conventional concrete also limits the varieties of fly ash which can be added to the compositions. For example, only so called "clean" fly ashes, such as those obtained from coal-fired power plants can be employed in conventional concrete mixtures. Fly ashes, which may contain organic or inorganic contaminants, such as those which are obtained from the combustion of refuse, cannot be employed, since such contaminants have a tendency to leach out of conventional concrete when it is subjected to rain or melting snow.
Finally, conventional concrete can be difficult to work with. After being poured, conventional concrete often requires significant screeting and troweling to obtain a smooth, usable surface. Furthermore, the tendency of conventional concretes to "bleed" water to the surface of the mass often aggravates the ability to obtain a smooth surface. In fact, if the surface of the concrete is troweled too extensively, it will dry to a loose, powdery mass which must be replaced.
Therefore, there is a need for cementitious compositions which exhibit substantially greater flexural, tensile and shear-bond strength, decrease permeability and which provide enhanced workability relative to cement compositions currently available.
There is also a need for methods of improving the flexural, tensile and shear-bond strength, and other desired properties of cementitious compositions and articles made from these compositions.
Accordingly, it is an object of the present invention to provide cementitious compositions which are substantially more flexible, tensile and shear resistant, less permeable, and provide enhanced workability than cement compositions previously known. Furthermore, it is an object of the present invention to also provide cementitious compositions which, through the preferred addition of sodium tripolyphosphate, also display many of the advantageous properties described in Applicant's U.S. Pat. No. 4,930,428.
In addition, it is also an object of the present invention to provide an aqueous premix for use in improving the flexural, tensile and shear-bond strength, as well as other desired properties, of cementitious compositions.
Finally, it is also an object of the present invention to provide a method of manufacturing shaped articles from the above compositions.